Long Term Evolution (LTE) supports data rates up to 100 Mbps in the downlink and 50 Mbps in the uplink. LTE-Advanced (LTE-A) provides a fivefold improvement in downlink data rates relative to LTE using, among other techniques, carrier aggregation. Carrier aggregation may support, for example, flexible bandwidth assignments up to 100 MHz. Carriers are known as component carriers in LTE-A.
LTE-A may operate in symmetric and asymmetric configurations with respect to component carrier size and the number of component carriers. This is supported through the use or aggregation of up to five 20 MHz component carriers. For example, a single contiguous downlink (DL) 40 MHz LTE-A aggregation of multiple component carriers may be paired with a single 15 MHz uplink (UL) carrier. Non-contiguous LTE-A DL aggregate carrier assignments may therefore not correspond with the UL aggregate carrier assignment.
Aggregate carrier bandwidth may be contiguous where multiple adjacent component carriers may occupy continuous 10, 40 or 60 MHz. Aggregate carrier bandwidth may also be non-contiguous where one aggregate carrier may be built from more than one, but not necessarily adjacent component carriers. For example, a first DL component carrier of 15 MHz may be aggregated with a second non-adjacent DL component carrier of 10 MHz, yielding an overall 25 MHz aggregate bandwidth for LTE-A. Moreover, component carriers may be situated at varying pairing distances. For example, the 15 and 10 MHz component carriers may be separated by 30 MHz, or in another setting, by only 20 MHz. As such, the number, size and continuity of component carriers may be different in the UL and DL.
As more than one component carrier may be used to support larger transmission bandwidths in LTE-A, a wireless transmit/receive unit (WTRU) may be required to feedback uplink control information (UCI) such as for example, channel quality indicators (CQI), precoding matrix indicators (PMI), rank indicators (RI), hybrid automatic repeat request (HARQ), acknowledgement/non-acknowledgement (ACK/NACK), channel status reports (CQI/PMI/RI), and source routing (SR) associated with downlink transmission for several component carriers. This means that the number of bits for UCI is increased compared to LTE. In addition, for uplink transmissions, the Peak to Average Power Ratio (PAPR) or Cubic Metric (CM) property needs to be considered. A large PAPR would cause the WTRU to back-off the power which would result in performance degradation. Accordingly, physical uplink control channel (PUCCH) transmissions need to have a low PAPR or CM.
In LTE-A, it is anticipated that the UCI overhead may be increased, compared to LTE, taking into account the new features including coordinated multipoint transmission (CoMP), higher order DL multiple-input multiple-output (MIMO), bandwidth extension, and relay. For example, in order to support high order MIMO (8×8 MIMO) and/or CoMP, a large amount of channel status reports (CQI/PMI/RI) are fed back to the serving base station and possibly neighboring base stations as well in CoMP. The UCI overhead will be further increased in asymmetric bandwidth extension. Accordingly, the payload size of Release 8 LTE PUCCH may not be sufficient to carry the increased UCI overhead even for a single DL component carrier in LTE-A. Therefore new methods are needed to carry UCI in a LTE-A carrier aggregation system.